Cathode for magnetron devices



1946 I. E. MOUROMTSEFF ETAL 2, 00,770

I CATHODE FOB MAGNETRON DEVICES- Filed Dec. 24, 1941 INVENTORS I. E.Mourom Ase ATTORNEY Patented May 21, 1946 Ni'l'E. stares cn'rnonn .ronAoNn'rnoN DEVICES Ilia Emmanuel Mouromtseif, Montclair, and John HamleyFindlay, Upper Montclair, N. J., as signors to. Westinghouse ElectricCorporation; East Pittsburgh, Pa; a corporation of PennsylvaniaApplication December 24, 1941, Serial No. 424,316

'7 Claims. (01. 250-275) electron emitting cathode axially sustainedtherein with both elements enclosed within an evacuated glass envelope.It is found in such devices that the portion centrally of the length ofthe cathode element of the tube reaches a higher equilibrium temperaturethan the end portions of the length of said cathode, to which severalreasons may be ascribed. One reason is that this central portion of thecathode is subjected to more severe electron bombardment than the endportions. Another reason is that the ends are more favorably situatedfor radiation. Yet another reason is that less bombardment occurs at theend portions than at the central portion. Bombardment results in theloss and destruction of the thermionically active material on thesurface of the cathode. Also the higher temperature of the centralportion of the cathode results in evaporation of the active material,and in either event the active material lost from the cathode is ingreater part found to be deposited on the inner concave face of theanode. This deposit on the anode materially interferes with theoperating characteristics of the magnetron device and shortens theoperating life and efficiency of. the device.

One of the objects of the present invention is to eliminate this defectin an electron discharge device of the magnetron type thereby toincrease the operating life and efiiciency of magnetron devices.

Another object is to provide an improved electron. emitting cathode fora magnetron device.

Still another object. is to provide an oxide coated cathode for anelectron discharge device of the magnetron type whichis notdeleteriously affected by electron bombardment.

Other objects and advantages will be apparent as the invention is morefully hereinafter disclosed.

In accordance with these objects, We have discovered that by locatingthe thermionically active material, adjacent the ends of the cathodeleaving the intervening or central area of the cathode bare and exposedto electron bombardment, the defect hereinabove noted, not onlyiseliminated but that theoperating characteristics of the device arestabilized and remain substantially con stant for relatively prolongedperiods of time as compared with devices provided with cathodes thatarethermionically active over substantially their entire length. Wehavefound that by 10- cating the thermionically active material on thecathode surface at a point remote from the area of intense electronbombardment and within the area wherein the temperature of the cathoderemains substantially constant, the amount of such material on thecathode may be reduced material- 1y to an amount required to produce asufficient quantity of electrons to initiate operation of the device andthat the secondary emission of the uncoated area produced by electronbombardment plus the electron emissivity of the electron emite tingmaterial on the cathode end portions is ample for continued operation ofthe device; and we have further found that by eliminating theevaporation of the electron emitting material onto the anode by solocating the electron emite ting material on. the cooler end portions ofthe cathode the operating characteristics of the device remain constantover a prolonged period of time as compared to prior art devices.

In accordance with these discoveries we have devised the electronemissive cathode of the type illustrated in the drawing for use inmagnetron devices.

Referring to the drawing 'l Fig. 1 is a sectional view of a magnetrondevice showing the essential elements thereof;

Fig. 2 is a cross-sectional view of the same along plane 22 of Fig. 1;

Fig. 3 is a sectional view of the improved electron emissive cathode ofthe present invention;

Fig. 4 is a cross-sectional view of the same along plane 4-4 of Fig. 3;and

Fig. 5 is a contemplated modification of the present invention.

As indicated in the drawin a magnetron device comprises a split anodeA'-A surrounding in the present instance an indirectly heated tubularcathode C sustained in concentric spaced relation within evacuated glassenvelope G by means of lead-in support wires a-a and 0-0, respectively,passing through press P of the envelope G. Magnetic coil M is providedto produce a magnetic field of the desired character within the device.

In accordance with the present invention, cathode C is shown ascomprising an elongated tubular metal base member It provided with aheater element H concentrically disposed therein as is customary in theart. A surfacecoatin E--E' of thermionically active material is presenton the outer surface of each end portion of the base Ill, extendinginwardly in each instance from the end portion towards the center adistance at least sufiicient to provide enough emission for energizationand actuation of the device. The active material is thereforeinsufficient in extent to be located upon the central area of the tubesubjected during operation to intense electron bombardment withconsequent high temperature and evaporation.

It is believed apparent that the amount of thermionically activematerial E-E' deposited on the end portions of base I of the cathode Cmay vary widely without essential departure from the present invention,depending upon the nature of material employed and upon the field of usefor which the device is designed. In general, the object is to locatethe thermionically active material E-E on th area of the cathode surfacewhich in the normal operation of the device has lowest temperature andis subjected to the least electron bombardment. This area obviouslyvaries with respect to the tube design, such as anode length andanode-cathode spacing and for devices where the electron bombardmentduring normal operation may extend over the greater portion of thelength of the cathode enclosed by the anode. It

is contemplated that the cathode C may be elongated at leastsufiiiciently to provide an area at each end that is beyond the area ofdisruptive electron bombardment upon which the electron emittingmaterial E-E may be located.

Irrespective of the fact that the electron emissive material E-E' islimited to the area of the base ill which is remote from the area ofintense electron bombardment, and at a temperature sub stantially belowthe vaporization temperature of the electron emitting constituentthereof, the exposed or uncoated area of the base it still functionsunder theinrluence of electron bombardment as anemitter of secondaryelectrons. Accordingly, base it may be comprised of any one of aplurality of metals and alloys heretofore known in the art to be ofutility as an emitter of secondary electrons under electron bombardment.Preferably, base if! is comprised of substantially pure nickel, butalternatively may be comprised of molybdenum or of one of the variousnickel alloys heretofore found satisfactory as a base met l forthermionically active oxide coatings for such cathodes.

Within the contemplation of the present invention also is the provisionof a cathode consisting of a tubular base it comprised of a metal ormetal alloy highly reactive as an emitter of secondary electrons underelectron bombardment but not necessarily suitable for use as a base forelectron emittin material EE wherein material EE' is located on sleevemembers 2 l--2 I comprised of material suitable for use as a base forelectron emitting material E--E and adapted to be slipped onto the endsof tubular base 29 substantially as indicated in Fig. 5.

Having hereinabove described the present invention generically andspecifically and described and illustrated one specific embodimentthereof, and for simplicity having omitted herefrom further illustrationand description of other modifications and departures from the preciseshowing herein, but which might have been included in substitution foror in addition to the selected showing, applicants do not disclaim anysuch modifications and departures as may fall within the scope of thefollowing claims.

base member, all active areas of the cathode being situated in the saidconcentrated field of the magnet.

2. A magnetron device having a magnet establishing a concentrated field,an anode having an electron-receiving face in said field and an envelopeenclosing the electron-receiving face of said anode, an electronemitting cathode Within said envelope and opposed to saidelectron-receiving face of the anode, said cathode consisting of anelongated metal base member having the thermionically active surfacearea thereof restricted to the area adjacent each end of the base memberand consisting of material resistant to eva orating under electronbombardment, all active areas of the cathode beingsituated in the saidconcentrated field of the magnet.

3. A magnetron device having a magnet establishing a concentrated field,an anode havingan electron-receiving face in said field and an envelopeenclosing the electron-receivin face of Said anode, an electron emittingcathode within said envelope and opposed to said electron-receiving faceof the anode, said cathode consisting of an elongated metal base memberhaving the thermionically active surface area thereof re stricted to thearea adjacent each end of thebase member, said base member in the areaintermediate said thermionically active end areas consisting of materialof relatively high secondary emissivity under electron bombardment, allactive areas of the cathode being situated in the said concentratedfield of the magnet.

4. An electron emitting cathode consisting of an elongated metal basemember having the thermionically active surface area thereof refacebeyond the area of intense electron bombardment and within the end areasof the said cathode.

5. A .cathode element consisting of an elongated tubular base consistingsuperficially in the center area thereof of material of relatively goodsecondary electron emissivity under electron bombardment and at each endthereof super ficially of material of relatively high primary electronemissivity, and means interiorly of said tubular base member to heat theend areas of the said tubular base member to the temperature of primaryelectron emissivity.

6. A cathode element comprised of an elongated tubular metal base memberconsisting of nickel, a thermionically active oXide coating dis posed onthe surface of said base member within the area adjacent each tubularend remote from electron. bombardment during operation, and heater meansdisposed Within the said tubular member to heat the end portions of thesaid tubular member to the temperature of electron emissivity of saidoxide coating thereon.

7. A magnetron device comprising an envelope, an anode in said,envelope, a magnet presenting a concentrated field within said anode, anelectroni emitting cathode in said field and anode, said cathodeconsisting of an elongated metal base member having the thermionicallyactive surface area thereof restricted to the area adjacent each end ofthe base member, said base member comprising an elongated metal tubeconsisting of substantially pure nickel and the said thermionicallyactive surface area adjacent each end of the tube comprising athermionically active oxide coating, said oxide coating being limited tothe area of said tube surface beyond the area of intense electronbombardment during operation of said device and within the end areas ofthe said cathode, and means within said envelope for thereby heating theend portions of the tube and thermionioally active coating on the endareas thereof to the temperature of electron emissivity of said 10coating.

ILIA EMMANUEL MOUROMTSEFF. JOHN HAMLEY FINDLAY.

